1. Field of the Invention
The present invention relates generally to decoupling the power-ground voltages of integrated circuits, and particularly to an improved buried capacitance for decoupling.
2. Background of the Invention
As frequencies in high speed electronic devices increase, decoupling power-ground voltages for devices becomes more challenging. Integrated circuits (ICs) require high frequency current for their operation. The current requirements for devices must be identified to properly assess the decoupling and power distribution requirements. The charging and discharging of capacitors is typically used to provide the needed supply for devices.
Often, electronic devices are mounted onto printed circuit boards (PCBs). A PCB power distribution system must provide sufficient current for the circuitry of devices on the PCB to operate. This includes high peak current requirements during output switching. The power distribution system must supply this current while maintaining the input supply voltage needed by devices.
To achieve this, discrete capacitors are often placed near the devices. These capacitors are connected between the power and ground planes to provide the necessary charge current to the devices. For example, these capacitors discharge their current into the device and quickly recharge from energy stored in slower discharging capacitors and power supplies prior to the next required discharge as needed by the device. The frequencies provided are often much higher than the IC primary clock frequency.
At high frequencies, power-ground planes and ceramic decoupling capacitors and a bulk decoupling capacitor are often used in combination. But as the required frequency increases, the ceramic decoupling capacitors must be located closer to the IC or other device they are decoupling.
To remedy this issue, buried capacitance was invented to alleviate the need for ceramic decoupling capacitors. Buried capacitance uses a combination of a thin dielectric material between power and ground planes and dielectric material with a relatively high dielectric constant. However, buried capacitance alone usually does not have the required current supply versus frequency response characteristics, and ceramic decoupling capacitors are usually still required.